# Maths Dispute



## Lorem Ipsum (Dec 13, 2008)

I was holding a quiz the other day, and this question came up:



> I walk to school every day. It takes me 20 minutes to do this. On the way home though, I run, and it takes me a quarter of this time. My school is exactly 1km away. On average, how fast am I travelling, in km/h?


Now, I gave the answer as 4.8, worked out by this method:

speed in km/h = distance/speed.

In this case it's 2/25. That's km/minute, so you need to multiply by 60, which is 120/25. That simplifies into 4 4/5, or 4.8.

Yet the other person in the quiz completely disagrees with the answer. He can't prove why, he just says it is wrong.

If somebody could clear this up, it would be much appreciated.


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## Seritinajii (Dec 13, 2008)

I'm not really sure, but the 2/25 to 120/25 might not really be right, since that would be multiplying the km you walk by 60, to me doesn't make much sense. I think you should make a proportion, figuring out how many km you could walk in 60 minutes, or one hour - 

2/25 = x/60 - 25x = 120. Bla bla bla, algebra, x equals... 4.8 again. Oh.

I don't know. D:


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## Rwr4539 (Dec 13, 2008)

As far as I can tell (my maths mind is fuzzy atm due to tiredness), that's right.

Tell him he's being stupid next time you see him.


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## Lorem Ipsum (Dec 13, 2008)

It's not multiplying the km you walk by 60, because 2/25 is the speed in km/minute; you multiply by 60 to get km/h.


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## opaltiger (Dec 13, 2008)

You're definitely right. The trick with this kind of question is usually people forget to take into account the time, and just take the average of the two speeds, but since you specifically have the time given here it's rather easy.


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## Lorem Ipsum (Dec 13, 2008)

Well, the dude said this:

"Due to the laws of various motion physics and speed averages, working out averages of speed is a lot more complex than meets the eye, and if any of you have done university level or higher level physics, you would know this. Otherwise, you are not in a position to respond, thank you."

He's talking out of his arse though; maths is what should happen, not what will happen


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## Lady Grimdour (Dec 13, 2008)

Lorem Ipsum said:


> Well, the dude said this:
> 
> "Due to the laws of various motion physics and speed averages, working out averages of speed is a lot more complex than meets the eye, and if any of you have done university level or higher level physics, you would know this. Otherwise, you are not in a position to respond, thank you."
> 
> He's talking out of his arse though; maths is what should happen, not what will happen


Ask him to prove this and see him make an ass of himself, one way or the other.


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## Lorem Ipsum (Dec 13, 2008)

Well, he's just admitted that I am right, but won't tell me how he came about this change of heart.


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## CNiall (Dec 13, 2008)

Lorem Ipsum said:


> Well, the dude said this:
> 
> "Due to the laws of various motion physics and speed averages, working out averages of speed is a lot more complex than meets the eye, and if any of you have done university level or higher level physics, you would know this. Otherwise, you are not in a position to respond, thank you."
> 
> He's talking out of his arse though; maths is what should happen, not what will happen


If anyone says that in a secondary school quiz you should be pretty wary. :\


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